The following abbreviations are herewith defined:
3GPP third generation partnership project
AT allocation Table (=PDCCH, on the L1/L2 control channel)
DL downlink
DL-SCH downlink shared channel of E-UTRAN
DRX discontinuous reception
eNB evolved nodeB (of an LTE system)
E-UTRAN evolved UTRAN
GSM global system for communications
IMSI international mobile subscriber identity (64 bits)
LA location Area
LTE long term evolution of 3GPP (3.9G)
Node B base station or similar network access node
OFDM orthogonal frequency division multiplex
PDCCH physical downlink control channel (L1/L2 control channel)
PG_RNTI/P_RNTI paging-RNTI
PLMN public land mobile network
RAT radio access technology
RNTI radio network temporary identifier (16 bits)
RRC radio resource control
SI-RNTI system information-RNTI
SIB system information block
SU scheduling unit
TA tracking Area
TTI transmission time interval
UE user equipment (e.g., mobile equipment/station)
UL uplink
UMTS universal mobile telecommunications system
UTRAN UMTS terrestrial radio access network
Relevant to this invention is the discontinuous reception DRX periods during which a mobile terminal or other user equipment is allowed to power down (sleep or idle mode) and the network knows not to send transmissions to that mobile terminal. Other active periods are synchronized to this DRX period, often to very close tolerances to avoid wasting air interface resources. For example, the network often will send a resource allocation (e.g., AT or PDCCH) to the mobile terminal in the transmission time interval immediately following the end of the terminal's DRX period. The DRX concept is an important power-conservation strategy for the mobile terminals, as their sleep or idle mode requires very little power.
The specific detailed description is in the context of 3.9G mobile communications, also known as LTE or E-UTRAN or system architecture evolution SAE. 3.9G is a radio access technology (RAT) planned as a new radio access replacing and upgrading the 3G WCDMA (wideband code division multiple access) UTRAN radio access network. Though described in view of 3.9G, many current wireless systems use the DRX concept and can benefit from these teachings, as will future systems that employ discontinuous reception at the mobile equipment. For example, the GERAN system uses a paging period (see 3GPP TS 45.002) and legacy UTRAN (3G) uses paging and idle mode DRX (see 3GPP TS 25.331 and TS 25.304).
FIG. 1 is a general overview of the DRX concept in E-UTRAN for a single mobile terminal. The physical downlink control channel PDCCH gives resource allocations (an AT) to multiple mobile terminals for resources in the uplink and downlink shared channels (shown as packet data channel PDCH). More than one consecutive PDCCH may be used (the duty cycle or ‘on-duration’) while in the RRC connected mode, but the overall schedule repeats after each DRX.
The LTE radio access network eNBs broadcast system information for terminals. System Information consists of NAS (Non Access Stratum) and AS (Access Stratum) system information. The AS part includes, among other information, idle and active mode system information which is needed in accessing the network including neighbor RAT and neighbor channel information and configuration of terminal measurements to be used in idle and active modes. The NAS portion includes, among other information, parameters of the LA, TA, PLMN identity and PLMN types that may be reached from the serving RAT.
The mobile terminal receives/reads the relevant system information of the serving eNB before accessing the system for several reasons. The system information enables the mobile terminal to optimize the radio access, to recognize if the cell access is restricted by the operator, and to determine if the terminal has access rights in the cell. The PLMN identity information tells if the network is the home network ora visited network, and gives the mobile terminal additional information.
But even if the mobile terminal (UE) has no need to access the system, it still needs to synchronize to the DL_SCH and align to the idle mode DRX of the eNB in order to receive possible paging messages from network.
One of the parameters needed in idle mode terminal is the idle mode DRX period so that UE and eNB have a synchronized paging occasion. Additionally, if grouping of UE paging messages is applied, there are further parameters concerning grouping information that all of the grouped UEs need for their idle mode. The current assumption in LTE is that paging indications are sent in the L1/L2 control channel (e.g., PDCCH, see FIG. 1) using a dedicated RNTI value. In various discussions this dedicated RNTI may be named P_RNTI or PG_RNTI. The UEs having a paging occasion at a predetermined time then check the L1/L2 control channel for the occurrence of the dedicated PRNTI/PGRNTI. If a P_RNTI/PG_RNTI match is found, the UEs proceed to read the paging message (e.g., on the paging channel PCH). Allocation for PCH is given in PDCCH and is mapped to the DL_SCH.
Now, a problem arises in the distribution of all of the DRXs of the various UEs relative to the DL_SCH. The DRXs for different UEs should be distributed such that the eNB scheduler has optimal access to the DL_SCH and is able to multiplex the PCH and all DL packet bearers.
In UTRAN (3G) the solution for the distribution has been based on a separate channel, termed the PICH or paging indicator control channel, and the assignment of the UEs to specific PICH bit positions by a mod formula with the IMSI. In UTRAN there is also a separate PCH channel and thus the paging does not use the general DL resources. In E-UTRAN, there is no PICH and the PCH is mapped to the DL_SCH with data for other UEs.
Three solutions have been proposed in discussions for LTE development. Document R2-071904 (3GPP TSG-RAN2 Meeting #58; Kobe, Japan; 7-11 May 2007) entitled “IDLEMODE PAGING” by Samsung proposes that there is no need for paging groups in LTE. Document R2-071926 (3GPP TSG-RAN2 Meeting #58; Kobe, Japan; 7-11 May 2007) entitled “TRANSMISSION OF LTE PAGING” by LG Electronics proposes to use paging groups indicated by redundant L1/L2 control channel bits. Document R2-071927 (3GPP TSG-RAN2 Meeting #58; Kobe, Japan; 7-11 May 2007) entitled “PAGING GROUP INDICATION” by IPWireless proposes that several paging groups can be indicated by having several hierarchical P_RNTI.
As discussed in document R2-072513 (3GPP TSG-RAN2 Meeting #58b; Orlando, USA; 25-29 Jun. 2007; entitled “IDLE MODE PAGING”; by Samsung), LTE offers a 10-fold increase in potential paging occasions as paging may be performed on subframe basis. More paging occasions per radio frame will allow for smaller paging groups and possibly smaller paging messages. This may lower the effort for the UE to decode the paging message. The signaling overhead however will increase. A low number of paging occasions per radio frame can reduce signaling and also simplify scheduler decisions at the cost of more UEs per paging group.
From a UE standby power consumption point of view, it is advantageous to have a specific frame or even subframe where the UEs can check their paging when in the idle mode. Presently LTE assumes that paging groups (where multiple UEs can be addressed) are used on the L1/L2 signaling channel, that the precise UE identity is found on the PCH, and that the idle period/DRX is UE specific.
In the LTE network there is no need to have any grouping for UEs except to help the Node B scheduler in sharing the DL-SCH for all U-plane (user) and C-plane (control) packet flows. In the UEs, paging groups may help in decreasing UE standby power consumption as the UE's reception period is statistically shorter when there are less frequent paging indications and thus less PCH access linked to the paging occasions.
There seems to be a consensus in LTE discussions that there will be at least one special P-RNTI value. UEs which detect the P-RNTI on the L1/L2 control channel in their particular paging occasion will then read the PCH. Proposals have been given to have multiple RNTIs for paging indications, and this RNTI set is divided among all the UEs.
It is anticipated that paging groups will continue to be a valuable option in LTE. What is needed in the art is a simpler implementation for paging groups in LTE, preferably without using the redundant bits in the L1/L2 control channel as in document R2-071926 and leaving those bits available for future use.